Activity-dependent induction of slow myosin gene expression in
isolated fast mouse muscle.
Barton-Davis, Elisabeth R., William A. Laframboise, and Martin J.
Kushmerick.
Departments of Physiology and Biophysics, of Radiology, of
Biochemistry and Center for Bioengineering, University of Washington,
Seattle, WA 98195
APStracts 3:0254C, 1996.
We demonstrate that direct electrical stimulation of isolated fast
muscle in an organ culture system can induce expression of the slow
myosin heavy chain (beta-MHC) gene indicative of a phenotype
transformation. Pairs of extensor digitorum longus (EDL) muscles were
isolated from adult mice, incubated at resting length in separate
chambers and superfused with the same recirculated media. One muscle
was subjected to twitch stimulation (5 second trains of 5 Hz pulses
at supramaximal voltage every minute), and force was recorded to
assess function. The contralateral muscle was incubated without
stimulation to control for effects of the experimental preparation.
Both muscles were rapidly frozen for RNA purification and oligo-dT
primed reverse transcription; serial studies were carried out to 36
hours. PCR was performed utilizing primers specific for beta
-cytoplasmic actin (beta-actin), a constitutive marker, and beta-MHC,
a gene which is either inactive or expressed at very low levels in
control EDL. After 30 hours of stimulation, beta-MHC was consistently
detected at a level several fold higher in stimulated EDL than in
incubated control EDL when band intensities were normalized to those
of beta-actin. These results show that signals for fiber specific
transformations reside within the muscle and that this shift begins
rapidly after induction of continuous stimulation.
Received 15 March 1996; accepted in final form 23 July 1996.
APS Manuscript Number C150-6.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 21 August 1996